Enters the ROI specification mode.
In this mode, an ROI frame may be specified by moving the mouse cursor over one corner of the desired ROI frame and dragging the mouse cursor (holding down the left mouse button) to the opposite corner. After the mouse button has been released, the ROI frame may be manipulated, using the frame handles. If the left mouse button is pressed outside the selected ROI, a new frame can be specified. If the left mouse button is pressed inside an ROI frame, it is selected as the active ROI. Activating this option displays the Select Region of Interest Dialog